1 files changed, 139 insertions, 0 deletions
diff --git a/web/api/queries/des/des.c b/web/api/queries/des/des.c
new file mode 100644
index 000000000..93d724723
--- /dev/null
+++ b/web/api/queries/des/des.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <web/api/queries/rrdr.h>
+#include "des.h"
+
+
+// ----------------------------------------------------------------------------
+// single exponential smoothing
+
+struct grouping_des {
+    calculated_number alpha;
+    calculated_number alpha_other;
+    calculated_number beta;
+    calculated_number beta_other;
+
+    calculated_number level;
+    calculated_number trend;
+
+    size_t count;
+};
+
+static size_t max_window_size = 15;
+
+void grouping_init_des(void) {
+    long long ret = config_get_number(CONFIG_SECTION_WEB, "des max window", (long long)max_window_size);
+    if(ret <= 1) {
+        config_set_number(CONFIG_SECTION_WEB, "des max window", (long long)max_window_size);
+    }
+    else {
+        max_window_size = (size_t) ret;
+    }
+}
+
+static inline calculated_number window(RRDR *r, struct grouping_des *g) {
+    (void)g;
+
+    calculated_number points;
+    if(r->group == 1) {
+        // provide a running DES
+        points = r->internal.points_wanted;
+    }
+    else {
+        // provide a SES with flush points
+        points = r->group;
+    }
+
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+    return (points > max_window_size) ? max_window_size : points;
+}
+
+static inline void set_alpha(RRDR *r, struct grouping_des *g) {
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+
+    g->alpha = 2.0 / (window(r, g) + 1.0);
+    g->alpha_other = 1.0 - g->alpha;
+
+    //info("alpha for chart '%s' is " CALCULATED_NUMBER_FORMAT, r->st->name, g->alpha);
+}
+
+static inline void set_beta(RRDR *r, struct grouping_des *g) {
+    // https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+    // A commonly used value for alpha is 2 / (N + 1)
+
+    g->beta = 2.0 / (window(r, g) + 1.0);
+    g->beta_other = 1.0 - g->beta;
+
+    //info("beta for chart '%s' is " CALCULATED_NUMBER_FORMAT, r->st->name, g->beta);
+}
+
+void *grouping_create_des(RRDR *r) {
+    struct grouping_des *g = (struct grouping_des *)malloc(sizeof(struct grouping_des));
+    set_alpha(r, g);
+    set_beta(r, g);
+    g->level = 0.0;
+    g->trend = 0.0;
+    g->count = 0;
+    return g;
+}
+
+// resets when switches dimensions
+// so, clear everything to restart
+void grouping_reset_des(RRDR *r) {
+    struct grouping_des *g = (struct grouping_des *)r->internal.grouping_data;
+    g->level = 0.0;
+    g->trend = 0.0;
+    g->count = 0;
+
+    // fprintf(stderr, "\nDES: ");
+
+}
+
+void grouping_free_des(RRDR *r) {
+    freez(r->internal.grouping_data);
+    r->internal.grouping_data = NULL;
+}
+
+void grouping_add_des(RRDR *r, calculated_number value) {
+    struct grouping_des *g = (struct grouping_des *)r->internal.grouping_data;
+
+    if(isnormal(value)) {
+        if(likely(g->count > 0)) {
+            // we have at least a number so far
+
+            if(unlikely(g->count == 1)) {
+                // the second value we got
+                g->trend = value - g->trend;
+                g->level = value;
+            }
+
+            // for the values, except the first
+            calculated_number last_level = g->level;
+            g->level = (g->alpha * value) + (g->alpha_other * (g->level + g->trend));
+            g->trend = (g->beta * (g->level - last_level)) + (g->beta_other * g->trend);
+        }
+        else {
+            // the first value we got
+            g->level = g->trend = value;
+        }
+
+        g->count++;
+    }
+
+    //fprintf(stderr, "value: " CALCULATED_NUMBER_FORMAT ", level: " CALCULATED_NUMBER_FORMAT ", trend: " CALCULATED_NUMBER_FORMAT "\n", value, g->level, g->trend);
+}
+
+calculated_number grouping_flush_des(RRDR *r, RRDR_VALUE_FLAGS *rrdr_value_options_ptr) {
+    struct grouping_des *g = (struct grouping_des *)r->internal.grouping_data;
+
+    if(unlikely(!g->count || !isnormal(g->level))) {
+        *rrdr_value_options_ptr |= RRDR_VALUE_EMPTY;
+        return 0.0;
+    }
+
+    //fprintf(stderr, " RESULT for %zu values = " CALCULATED_NUMBER_FORMAT " \n", g->count, g->level);
+
+    return g->level;
+}